The invention relates to a system and method for controlling fuel vapor purging in a vehicle equipped with an internal combustion engine coupled to a fuel tank coupled to a purging canister.
Vehicles typically have various devices installed for preventing and controlling emissions. One of the sources of emissions are fuel vapors generated in the fuel tank due to temperature cycling and fuel vapors that are displaced in the process of refueling the fuel tank. In order to remove these vapors from the fuel tank, vehicles are equipped with fuel emission control systems, typically including a fuel vapor storage device, which in this example is an activated charcoal filled canister for absorbing the evaporative emissions. One such system is described in U.S. Pat. No. 5,280,775. The canister is connected in series between the fuel tank and the engine. Vapors generated in the fuel tank are drawn into the canister where the fuel component (usually hydrocarbons) is absorbed on the carbon granules and the air is expelled into the atmosphere. A solenoid controlled, constant pressure operating valve is fitted in a passage between the canister and the fuel tank to selectively enable and disable communications. Also, a purge control valve is located in the passage between the engine and the canister. During canister purge, the valve opens, allowing manifold vacuum from the engine to draw air from the atmosphere back into the canister, thus purging the fuel vapors into the engine, where they are burned.
Other conventional systems have a three-way connection between the fuel tank, the canister, and the engine as described in U.S. Pat. No. 5,048,492. The engine is connected to the fuel tank and the carbon canister via a communication passage. A purge control valve is located in the intake manifold of the engine. A controller selectively opens and closes the purge control valve to allow purged fuel vapors to enter the engine.
The inventors herein have recognized a disadvantage with the above approaches. Namely, with the first system, the vapors are always pushed through the canister in one direction, in at one end and out at the other, which means that sediments do not get removed from it by opposing airflow. In other words, pushing the vapors in only one direction may prematurely degrade the canister and reduce the durability of the canister. With the second system, there is a risk of rich or lean spikes or air and fuel vapors inducted into the engine during canister purging since the tank is not isolated. These vapor transients can cause vehicle stalls or degrade emission control. Another disadvantage is that under certain conditions, with the vapors from the fuel tank always entering the canister, the rate of fuel vapor generation may become greater than the rate of purge into the engine. Consequently, the carbon canister may become saturated and the fuel purge may take a long time to complete. This disadvantage is exacerbated in vehicles with direct ignition spark injection (DISI) and hybrid electric vehicle (HEV) engines. In DISI engines fuel is sprayed directly into the engine cylinder, and they frequently operate with low or no vacuum. An HEV engine is typically an electric motor coupled to a conventional internal combustion engine that is periodically turned on and off. In both DISI and HEV engines, the fuel vapor purge cycle is much shorter than in conventional engines. However, with the second system, a large amount of purge time is required due to the fact that the fuel tank is not isolated and vapors are always being generated, thereby limiting potential fuel economy benefits.
An object of the present invention is to provide a system for improved control of fuel vapor purging in to an internal combustion engine.
The above object is achieved and disadvantages of prior approaches overcome by a system for controlling fuel vapor purging in a vehicle consisting of: an internal combustion engine; a fuel tank; a fuel vapor storage device; and a valve assembly routing fuel vapors in a first direction only from said fuel tank to said fuel vapor storage device and for routing fuel vapors in a second direction opposite said first direction into said engine only from said fuel vapor storage device.
An advantage of the above aspect of the invention is that the proposed system configuration allows isolating the fuel tank during canister purging. This eliminates fuel vapor transients from the tank to the engine. With the tank isolated, vehicle stalls or emission control degradation can be minimized. Also, this system achieves the benefits of in-series canister buffering without the durability problems associated with prior approaches. In addition, by allowing the canister to be filled in one direction and purged in the opposite direction, the time required to purge fuel from the canister can be reduced by not requiring fuel vapor to be drawn through all the canister""s active carbon. Another advantage is with the proposed configuration purge time will be reduced due to the fact that that fuel tank vapors will not continuously be entering the canister.
Other objects, features and advantages of the present invention will be readily appreciated by the reader of this specification.